TO DISCOVER MARK THORNTON’S AFRICA, YOU MUST FIRST ALLOW YOURSELF TO GET LOST.

Big, pristine wilderness “where no others go.”

Put away your smartphone. Leave the creature comforts of the SUV.

Thornton’s adopted continent of 25 years is best experienced on foot, from the cacophony of its wildlife and vast terrain to the rhythms of nature and the warmth of its people.

His company, Mark Thornton Safaris, specializes in walking and wilderness camping expeditions in the Serengeti, Tarangire, and Ruaha national parks, as well as the Maasai Steppe in northeastern Tanzania. One of the guiding principles of his business is “We go where no one goes.” Encountering a lion or an elephant on a walking safari—albeit from a safe distance—is unlike anything else. “When you’re on foot everything’s different,” Thornton says. “It’s real.”

Thornton says there is a fundamental respect for the boundaries of the animals’ natural habitat that comes from years of experience possessed by him and his three fellow guides, who are like family members.

“It’s not about, let’s see how close we can get and push the envelope,” he says. “When you’re out there walking, there is an anticipation and excitement.”

Thornton first visited Africa as part of a semester abroad program during his senior year at the University of Richmond, where he studied wildlife ecology and conservation. After college, he returned to work as an operations manager for a safari company.

“I got exposed to walking safaris,” he says. “Then that changed everything. It really kind of clicked with what a real safari is like.”

A beautiful leopard near camp.

Like many other popular tourist destinations, Africa has its share of “run-of-the-mill” safari outfits, according to Thornton, who started his own guide company about 20 years ago. The company creates custom itineraries for its clients based on their preferences, physical abilities, budget, and timetable. The starting price point for a safari package, detailed on thorntonsafaris.com, is about $800 a day per person. Thornton also offers offer non-walking trips. “There could be a really great person who says, ‘My knees are shot. I can’t really walk a lot.’ Or ‘My wife’s not going to stay in that adventure tent,’” he says.

The vast majority of Thornton’s clients are from the United States and Canada. There are first-timers. Young and old. Families who want more creature comforts. And then there are those who just can’t get enough of Africa. “I’ve had clients who have come back every year for eight years,” Thornton says. “It’s really nice because they become friends.”

Thornton’s safari business is based in the city of Arusha in northern Tanzania, which is a popular jumping-off point for visitors to the Serengeti and Mount Kilimanjaro. Many of them are drawn to the Serengeti for the great wildebeest migration, an annual caravan of two million grazers that crosses northern Tanzania and southern Kenya. About one third of the national park is generally off-limits to tourism, but Thornton’s company has been granted access to some of those untouched areas because its walking safaris have a much lower impact on the ecosystem. It would be like having a swath of Yellowstone National Park all to yourself, Thornton says.

Ever-busy banded mongooses at their den.

“So it’s kind of the purist, leave-no-trace, sustainable safari,” he says. “There’s been a lot of encounters over the past 25 years, whether it’s walking into lions or having those amazing experiences with elephants where you’re close and looking at each other. What really moves us the most is still being able to camp in areas that are not compromised, areas that are pure wilderness. That’s the thing that makes us the happiest.”

There are no roads or lodges to speak of in the “bush,” where wildlife sightings include zebras, leopards, giraffes and the fringe-eared oryx, which is a type of antelope. The Serengeti is also known for termite mounds, which are made of mud and held together by termites’ saliva. Forget about Wi-Fi. “You get some high-powered people who are on call 24 hours a day, and Day 7 they come up and say, ‘Mark, you know what? I haven’t been on the device in seven days.” Thornton and his fellow guides are permitted to carry heavy rifles, though they are a last resort for safety. Each has years of training. “You’re not just going to walk off into the Serengeti unless you have a good crew,” he says. Thornton’s adopted home served as inspiration for his novel, Kid Moses, which is about a boy who wanders the East African wilderness. Thornton lives with his wife and two young daughters in the forest outside Arusha. Every summer for one month, the family returns to New York City for vacation and to reconnect with family and friends stateside. “You’re gonna laugh. They want to go ride the subway,” he says of his daughters.

Thornton serves on the board of the Dorobo Fund, a nonprofit conservation group dedicated to protecting the cultures, people, landscapes, and biodiversity of Tanzania. His clients often leave the country with a newfound appreciation for the people.

“I think that people are coming here thinking about wildlife and they leave thinking about how warm and friendly Tanzanians are. Without sounding corny or clichéd,” Thornton says, “you’re out there in the bush together.”